The invention relates to a fan with an essentially square housing and an impeller that is centrally driven by an electric motor; with the axis of rotation of the impeller being perpendicular to a first main inlet surface of the housing and in parallel to the inflow direction. The flow of air leaving the impeller being deflected by 90.degree. leaving the fan housing at at least one lateral surface of the housing that is perpendicular to said first main surface; and wherein a bottom surface of said housing that is opposite the inlet surface being developed as a closed wall with the blade edges of the impeller on the outlet side being spaced a distance away from the bottom surface.
Initially fans were equipped with so-called radial impellers; i.e., the air is deflected in the impeller itself from the intake direction by 90.degree. into the outlet plane. This results in a higher pressure yield than by means of the so-called axial impeller fans. Fans of this type are known from the German Published Patent Application 22 57 509 (DE-413). Similar fans are also known from DE-OS 21 39 036 (DE-409). In both cases, a conventional radial impeller was used in which the 90.degree. deflection of the flow takes place inside the impeller.
However, solutions of this type (conversions of axial to radial flow) are also known where a deflection of the flow takes place in the area of the impeller itself although the shape of the impeller is that of an axial wheel.
Thus, it is stated in DE-AS 15 03 609 that the delivered medium is already subjected to a deflection in the first part of the impeller wheel and leaves the impeller wheel with a radial flow component. According to the objective that is described there, this solution seems to be useful mainly for very high pressure requirements. This prior solution also has a housing ring that expands conically in the direction of the flow delivery and extends approximately to over half the axial width of the impeller wheel. Because of this lack of complete covering of the axial width, the solution permits the radial flow component in the area of the impeller wheel. As far as the reduction of noise is concerned, this solution is still very imperfect.
Another previously known solution according to DE-OS 18 02 523, like the last-described arrangement, as far as the outward appearance is concerned, shows an axial impeller, but here also, the ring that surrounds the impeller extends only to the axial center of the impeller, so that a deflection of the air in radial direction takes place inside the impeller. In axial view, this arrangement is very large.
DE-PS 634 449 shows a spiral housing where the deflection of the air flow in radial direction takes place by means of very rounded blades in their central area. The impeller that is used here is also an axial wheel, but the blades themselves deliver air radially beyond their outer edges into the flow space-analogously to the two last-described solutions. The tube that extends from an inlet plane into the axial center of the blades and encloses it is tapered extensively in flow direction.
In all these previously known solutions, the blades have the function to deliver extensively in radial direction via their radially exterior blade edges, and the deflection of the air takes place, as in the case of the conventional radial impeller, inside said impeller. These solutions are not suited to sufficiently satisfy today's predominant objective of low noise while still retaining an axially compact fan.
In the electronics industry or in the data-processing industry, it is also common to use fans of this type in connection with larger housing boxes for the ventilating of the electronic system located in the apparatus. It is increasingly required in these cases that the noise level be low, particularly in the field of miniature fans having impeller diameters of less than 200 mm. In practice, the situation exists that more compromises can be made with respect to the pressure or volume per time, while very strict requirements exist with respect to noise levels. The result is that frequently fans of this type are operated at lower rotational speeds only for noise reasons. Thus, the constant demand with respect to a "noise minimization" is a predominant aspect in the development of fans of this type.
Within the scope of this objective, it was surprisingly found that a fan with an essentially square housing and an impeller that is centrally driven by an electric motor; with the axis of rotation of the impeller being perpendicular to a first main inlet surface of the housing and in parallel to the inflow direction. The flow of air leaving the impeller being deflected by 90.degree. leaving the fan housing at at least one lateral surface of the housing that is perpendicular to said first main surface; and wherein a bottom surface of said housing that is opposite the inlet surface being developed as a closed wall with the blade edges of the impeller on the outlet side being spaced a distance away from the bottom surface is effective in its performance and extremely low in noise.
Thus, it was found, for example, that a fan that is constructed according to the state of the art, with rectangular parallelepiped dimensions of approximately 130.times.130.times.40 mm and was equipped with a conventional radial impeller, with respect to noise, was reduced to 44 dba by means of special measures, whereas the fan according to the invention, with the same dimensions and equipped with an essentially square housing and an impeller that is centrally driven by an electric motor; with the axis of rotation of the impeller being perpendicular to a first main inlet surface of the housing and in parallel to the inflow direction. The flow of air leaving the impeller being deflected by 90.degree. leaving the fan housing at at least one lateral surface of the housing that is perpendicular to said first main surface; and wherein a bottom surface of said housing that is opposite the inlet surface being developed as a closed wall with the blade edges of the impeller on the outlet side being spaced a distance away from the bottom surface, and wherein the impeller is an axial impeller of the type that has an air-guiding outlet duct that is formed by a wall that radially on the outside completely surrounds the blades and where the air flow leaves the outlet edges of the impeller only in an axial direction, reduced this value to 38 dba. (This applies to both embodiments.) Naturally, comparable pressure and volume capacities exist in each case. Thus, in these operating cases, the pressure is relatively low and the volume is moderate, thus, in the case of the characteric pressure-volume curve, mainly in the medium range, at least on the right of the salient stability point of the characteristic pressure-volume curve, air flow has not yet "broken off".
Other advantageous developments are found with an essentially square housing and an impeller that is centrally driven by an electric motor; with the axis of rotation of the impeller being perpendicular to a first main inlet surface of the housing and in parallel to the inflow direction. The flow of air leaving the impeller being deflected by 90.degree. leaving the fan housing at at least one lateral surface of the housing that is perpendicular to said first main surface; and wherein a bottom surface of said housing that is opposite the inlet surface being developed as a closed wall with the blade edges of the impeller on the outlet side being spaced a distance away from the bottom surface. The impeller is an axial impeller of the type that has an air-guiding outlet duct that is formed by a wall that radially on the outside completely surrounds the blades and where the air flow leaves the outlet edges of the impeller only in axial direction and has the impeller diameter approximately 20% or 30% smaller than the outer side dimensions of a rectangular parallelepiped housing. Also advantageous is having the impeller with its blade edges that are located on the inlet side, disposed in the area of the air inlet plane as well as having the impeller blade edges of the axial impeller located on the outlet side, disposed approximately in the center of the axial height of the fan. It was also found advantageous to have, at the area of the air inlet blade edges of the axial impeller, a housing radially directly outside the impeller, with rounding at its inlet, as well as in the area of the outlet blade edges of the axial impeller, having the housing have a rounding, radially outside the impeller, so that the air after leaving the axial impeller at first encounters an enlarged flow cross-section. This enlarged flow cross-section can be caused by a diameter that is at least about 10% larger than the outlet and is formed over the whole circumference thereof. Another advantage of the invention is to have the blades of the impeller extend at least over half the axial height of the fan. Still further, it was advantageous to have the impeller blades take up, one half to one third of the axial height of the fan, with an outlet of the fan extending from the end of the impeller to the bottom wall and amounting to one half to one third of the axial height of the fan. Also it is advantageous to have the height of the housing be about 1/3 of the impeller diameter. Additionally, it was found advantageous to have the interior surface surrounding wall of the housing defining the outlet of the fan to be an essentially cylindrical flow ring.
Probably, the advantageous effect can be expected not only in the case of a miniature fan of the type described in the following, but bascially also in the case of a larger construction. However, surprisingly, at least in the case of this miniature size, the combination according to the invention has proven to be extremely effective with respect to a minimizing of noise.